Device and process for the remelting of glass

ABSTRACT

The invention relates to a device for the remelting of glass bars:  
     with at least one receiving shell, which has an inlet at its upper end for the receiving of the glass bar, and an outlet at its lower end for the letting-off of melt;  
     with a crucible which is located underneath the receiving shell, is open at the top, and has a runoff at the bottom;  
     with a heating arrangement for heating the contents of the crucible;  
     for the avoidance of a tapering of the glass stream the under-edge of the receiving shell is located at the level of the liquid surface or higher;  
     after the crucible there is engaged a

[0001] The invention relates to a device and to a process for theremelting of glass semifinished products. It is a matter here of glasssemifinished products that are present in the form of bars. The barshave mostly a circular cross section. The remelting of such glasssemifinished products is necessary for the further processing. It isassociated mostly with a portioning of glass.

[0002] In principle glass--either pre-portioned or in relatively largequantities--can be melted with the necessity of a subsequent portioning.

[0003] The process of the remelting of portioned glass is problematical.From a certain temperature onward, namely, there occurs an adhesion ofthe glass to the underlayer or, respectively, to the forming tool. Theco-called adhesion temperature (10¹⁰ dPas) lies below the softeningtemperature (10^(7.6) dPas), so that in the remelting there occurs aadhesion of the glass to the wall of the melting vessel.

[0004] There could be considered cooling the wall, so that in the wallzone the adhesion temperature is not reached. But in the heating-upprocess the cooling cannot be strong enough for the contact temperatureto remain below the adhesion temperature. Furthermore, there occurexcessively great inhomogeneities of the temperature.

[0005] As remedy, work is being done with separating agents of varioustype. These lead, however, to undesired alterations of the glasssurface.

[0006] The other possibility lies then in melting larger quantities andthen portioning them. There the glass semifinished product is usuallyprepared not in the form of regular bodies, but it can be melted-up inthe crucible as glass fragments. In the first place, however, thisprocess is in general a discontinuous one; continuous processes requirespecial measures and therewith special expenditures. In the secondplace, here in all cases hollow-space forms, which are filled with airor another gas. To the glass fragments adsorbed gas adheres. When thefragment surfaces pass into the melt, then the adsorbed gas is releasedfrom the fragment surfaces, and bubbles form. In order to remove thesebubbles again from the melt, a strong increase of the melt temperatureto refining temperature is necessary. This means that the meltingprocesses must be run through once again. This is highly unfavorable anduneconomical energy-wise.

[0007] It is also possible, when using glass bars, to heat up the freebar end and therewith to do the melting. There, to be sure, theabove-mentioned problems do not arise. Here, however, there occurs acontinuous run-off of the glass in the form of a downward-tapering glassstream. A drop-portioning is not possible.

[0008] JP 63/236729A shows a device with which a glass fiber is drawn.At the outlet of a revolving nozzle there arises a “draw onion”(Ziehzwiebel). This device, therefore, does not serve for the remeltingand portioning of glass bars.

[0009] Underlying the invention is the problem of providing steps withwhich a remelting and portioning of glass semifinished material ispossible without there arising the problems of adhesion, of alterationof the glass surface, or of the gas inclusion; further, an energy-wiseand economically favorable process is to be given, with whichsemifinished material can be rewarmed and made available for theshaping.

[0010] This problem is solved by the independent claims. The solution isvery simple and requires a relatively slight expenditure.

[0011] One proceeds, accordingly, from a receiving shell which has anupper receiving opening for the introduction of a glass bar, and a loweroutlet opening. To the shell there is assigned a crucible. The crucibleis open at the top, so that the shell can plunge, at least in a part ofits length, into the space enclosed by the crucible wall. The cruciblehas a runoff in its lower region. There, any type of crucible heating ispossible, for example a resistance heating and a radiation heating. Anadvantageous form of execution is the providing of a coil whichsurrounds the wall of the crucible in a known manner. The coil servesfor the coupling of electric energy into the crucible contents.

[0012] The shell is suitably designed and dimensioned in such mannerthat its inner contour corresponds to the outer contour of the glassbars to be processed. The shell does not absolutely have to be vertical.It can also be slanted with respect to the vertical. Furthermore,instead of one shell there can also be provided several shells.

[0013] By corresponding allocation of shell and crucible it is achievedthat the glass bar in the shell melts at its lower end. In the crucibleitself there was previously melted up a glass bath. The glass bar meltsoff slowly at its lower end. The melting-off and flowing-off materialpasses continuously into the bath mentioned, present in the crucible.

[0014] When energy costs play no role, then the semi-finished productscan simply be melted up again below, refined at low viscosities and thenfed to the shaping operation. This heating to melting or refiningtemperature can be eliminated by the invention. The advantage becomesclear if one considers that the refining temperature can lie at ca.1600° C., for the shaping, however, only temperatures on the order of1100° C. are necessary.

[0015] What is essential for the device in its general form is merelythat the receiving shell be arranged over a container that contains aglass melt. The glass melt is portioned-- possibly only after furthertransport. Also an intermediately engaged homogenization step isconceivable. This becomes necessary if the introduced glass is a glassother than that which is present in the container.

[0016] An essential advantage of the process of the invention for theremelting and portioning is the continuity through the steadyfollowing-up of the glass bars. There the shape of the glass bar ends tobe added to one another is decisive in respect to the avoiding orminimizing of bubble inclusions.

[0017] Untreated bar ends, by reason of shrinkage in the production,have a concave curvature. The setting on one another of two such endswould lead to a gas inclusion in the cavity arising between the ends,which would later become visible in the feeder as bubble thrust,therefore spoilage.

[0018] A bar end is easily influenceable by the casting mold used forthe production. The shaping of the (other) bar end must occur bymechanical reworking and is expensive. But at least it is possible, ifnecessary, to free it from the concave curvature in this way. Assuitable pairs of bar ends there have proved the combinations in whichthe gas to be expelled can escape and is not trapped.

[0019] If the same amount of melt that is removed in a portioned manneris added to the crucible, then the volume of the melt in the crucibleremains constant. The level of the melt, therefore, likewise remainsconstant. If these conditions are maintained, then no level re-settingof the receiving shell is necessary.

[0020] For reasons of energy saving the volume of the crucible should bejust as great as that of the required portions being processed. Anyincrease of this volume is unfavorable in respect to the energy savingof the process.

[0021] The invention is explained in detail with the aid of the drawing.The drawing shows in vertical section an arrangement for the remeltingof glass bars.

[0022] There is perceived in particular the following:

[0023] A receiving shell 1 is provided. This is vertically arranged inthe present case. It is open at the top for the reception of a glass bar2. At its lower end it is first tapered into a truncated conical part1.1 and then goes over into a cylindrical part 1.2.

[0024] A crucible 3 is further provided. The crucible is pot-shaped. Ithas a bottom 3.1 as well as a cylindrical wall 3.2. The crucible has inits bottom a runoff in the form of a runoff shell 3.3. To the runoffshell 3 there is assigned a heating arrangement 4.

[0025] The cylindrical wall 3.2 of the crucible 3 is surrounded by amedium frequency coil 5. Over this coil electric medium-frequency energyis coupled into the crucible contents. Through the warmed crucible walland the warmed glass bath the receiving shell 1 is warmed by heatradiation over the crucible wall and the glass bath, especially itslower region.

[0026] The receiving shell 1 is produced in the present case fromplatinum with a wall thickness of 1 mm. The receiving shell isadjustable in its height. The melt-off amount is regulated over theheight adjustment of the receiving shell 1.

[0027] The device of the invention operates as follows:

[0028] Into the receiving shell 1 there is introduced a glass bar 2. Theinner contour of the receiving shell 1 and the outer contour of the gasbar are such that the glass bar 2 is snugly enclosed by the receivingshell 1. The temperature generated by the coil 5 in the crucible 3 iscontrolled in such manner that the glass bar 2 melts at its lower endand supplies the melt bath 7 setting in a controlled manner withafter-flowing glass. There the lower end of the receiving shell,especially the zone of the truncated conical part 1.1 and of thecylindrical part 1.2 is heated by the radiant heat from the wall 3.2 ofthe crucible 3 as, well as by the liquid level surface 7.1 of the meltbath. Also the receiving shell 1 can be adjusted in its height. Theunder edge of the receiving shell will have, as a rule, a distance of 1to 2 cm from the surface 7.1 of the melt bath. Even a plunging of thecylindrical part 1.2 into the melt bath 7 is thinkable. In accordancewith the distance, the melt-off performance and therewith the throughputcan be varied.

[0029] The glass bar 2 sinks by its own weight deeper and deeper intothe receiving shell 1, until it is largely melted up. Before it iscompletely melted up, a following glass bar can be introduced from aboveinto the receiving shell 1. The glass melt can thereby continuously beprovided with glass. The runoff shell 3.3 of the crucible may beequipped with a needle feeder arrangement. Therewith it is possible tocontrol the glass throughput throughout the device in a desired manner.The runoff shell 3.3 may also be provided with a shearing device inorder to generate glass drops for the following production steps.

[0030] The device can be used everywhere where, for a followinghot-shaping process there is needed glass which must be brought to hightemperatures lying above the adhesion temperature. With the device thereare avoided all the problems of the state of the art. There does notoccur any adhesion of glass to the walls of a shaping arrangement. Noseparating agent is needed. The glass surface is subject to noalteration. No after-engaged refining process is needed.

[0031] The device represented comprises a needle feeder 6.

[0032] The crucible represented in the present case is a platinumcrucible. The induction heating has a power of 10 kHz. Instead of thisthere would also be conceivable a 50 Hz resistance heating or aradiation heating.

1. Device for the remelting of glass bars (2); 1.1 with at least onereceiving shell (1) which has an inlet at its upper end for thereceiving of the glass bar (2), and an outlet at its other end for therunning-off of the melt; 1.2 with a crucible (3) which is locatedunderneath the receiving shell (1), is open at the top and has a runoff(3), at its bottom; 1.3 with a heating arrangement (5) for heating thecrucible contents; 1.4 the under-edge of the receiving shell (1) islocated, for the avoidance of a tapering of the glass stream, at theheight of the liquid level (7.1) of the melt bath (7) or above it; 1.5following the crucible (3) there is engaged a runoff shell (3.3); 1.6 tothe runoff shell (3.3) there is assigned an arrangement for thegeneration of drops (needle or suction feeder).
 2. Device according toclaim 1 , characterized in that the heating arrangement for the heatingup of the crucible contents comprises a coil (5) for the coupling-in ofelectric energy.
 3. Device according to claim 1 or 2 , characterized inthat the receiving shell (1) and the crucible (33) are arrangedrelatively to one another in such manner that the receiving shell (1) isenclosed by the crucible wall (3.2) at least on the lower part of itslength.
 4. Device according to one of claims 1 to 3 , characterized inthat the outlet zone (1.1, 1.2) of the receiving shell (1) is taperedcontinuously or abruptly in the running out direction.
 5. Deviceaccording to one of claims 1 to 4 , characterized in that the crosssection contour of the inner surface of the receiving shell (1) is atleast approximately equal to the cross section contour of the outersurface of the glass bar (2).
 6. Device according to one of claims 1 to5 , characterized in that the heating arrangement (4) is assigned to therunoff shell (3.3.).
 7. Device according to one of claims 1 to 6 ,characterized in that the runoff shell (3.3) is offset with respect tothe receiving shell (1).
 8. Device according to one of claims 1 to 7 ,characterized in that the receiving shell (1) is adjustable i n itsposition relatively to the crucible (3), especially in its height. 9.Process for the remelting of glass bars, with the following features:9.1 A glass bar (2) is introduced into the upper end of a receivingshell (1); 9.2 underneath the receiving shell (1) there is madeavailable a molten bath (7) with a surface (7.1); 9.3 the receivingshell (1) is positioned in such manner that its lower edge is located atthe height of the surface (7.1) or above it; 9.4 the lower end of theglass bar (2) is heated to a temperature above the softening temperatureof the glass; 9.5 the melt-off process is controlled in such manner thata continuous melt stream enters the molten bath (7) with avoidance of aconstriction; 9.6 melt is drawn off from the molten bath (7) by means ofan arrangement for drop generation.
 10. Process according to claim 9 ,characterized in that the melting-off of the glass bar (2) is performedby the coupling of electric energy into the crucible unit or byradiation heating elements, or by burner (blowpipe) heating.
 11. Processaccording to claim 9 or 10 , characterized in that the glass throughputis controlled by the means that at least one of the following parametersis altered: by the amount of the supplied energy; by the spacing betweenthe under edge of the receiving shell (1) and the liquid surface (7.1)of the molten bath (7); by a choking of the glass stream emerging fromthe bath (7).
 12. Process according to one of claims 9 to 11 ,characterized in that the glass bars (2) used have in each case at leastone end which closes off with a convex form (for example a cone, ahemisphere) or with a flat surface, in order to avoid an inclusion ofgas at the bar-to-bar impact point.